1. Field of the Invention
The present invention relates to a light emitting diode (LED) circuit, and more particularly, to an LED driving circuit directly applicable to an alternating current (AC) power without requiring a converter for converting the AC into a direct current (DC), and an LED array apparatus.
2. Description of the Related Art
A semiconductor light emitting diode (LED) is advantageous as a light source in terms of output, efficiency or reliability. Thus, the LED is actively researched and developed as a high-output and high efficiency light source to substitute a backlight of a lighting device or a display device.
In general, the LED is driven in a low driving current (DC). Therefore, to be driven at a normal voltage, i.e. alternating current (AC) of 220V, the LED requires an additional circuit, e.g., AC/DC converter for supplying a low DC output voltage. However, such an additional circuit complicates configuration of an LED module and furthermore potentially undermines efficiency and reliability when a supply power source is converted. Moreover, the additional part other than the light source increases costs and size of the product and also degrades electromagnetic interference (EMI) characteristics due to a periodic component when operating in the switching mode.
To overcome this problem, various types of LED driving circuits capable of being driven without an additional converter have been suggested. However, in a conventional AC-driven LED driving circuit, most LEDs are arranged to be driven in a specific half cycle of the AC voltage, thereby increasing the number of LEDs required for achieving desired light amount.
The necessary number of LEDs may be varied according to arrangement of the LEDs even though identical light amount is supplied. But the conventional arrangement of LEDs ensures very low efficiency. For example, in a conventional representative example where the LEDs are arranged in a reverse parallel or bridge configuration, the actual numbers of LEDs continuously emitted represent merely 50% and 60% of total numbers of LEDs, respectively. That is, a greater number of LEDs are inefficiently required to attain desired emission.
Therefore, the LEDs may be more efficiently arranged to assure identical light amount through a smaller number of LEDs. This arrangement with greater efficiency is of significant importance to assure cost efficiency of the AC-driven LED circuit.